textproduct: Albany

WHAT HAS CHANGED

Increased winds for Monday as winds shift to the northwest in the wake of the incoming cold front and become rather breezy with gusts up to 25-30kts. Otherwise, no major changes for the heavy rain potential for tonight into tomorrow but the marginal severe thunderstorm risk for tomorrow was expanded into the Capital District, most of western New England and into parts of the Upper Hudson Valley.

KEY MESSAGES

1) A slow moving cold front will result in periods of showers and thunderstorms across the entire region tonight into Monday. Heavy rainfall rates can result in isolated to scattered flash flooding, with areas that saw high rainfall amounts recently most susceptible to renewed flooding.

2) There is a marginal risk (level 1 of 5) for severe thunderstorms tomorrow afternoon for all of eastern NY and western New England, except the southwest Adirondacks and Mohawk Valley, with damaging winds the primary hazard.

DISCUSSION

KEY MESSAGE 1...

Latest satellite imagery shows a vertically stacked cut-off low in the Ohio Valley, approaching shortwave into the Great Lakes and strong ridging off shore supporting a deep fetch moisture from the Gulf and western Atlantic up the East Coast. This meridionally flow pattern will result in a highly moisture rich and humid environment across the Northeast through tomorrow as anomalously strong V-wind components allow PWATs to surge impressively towards 2-2.25" or 3 standard deviations above normal per the ENS standard anomalies. As the northern stream shortwave tracks into the Great Lakes today, it looks to slow down as it interacts with the closed low and amplify as it takes on a negative tilt through tonight. With this shortwave displaced well to our west and weak subsidence still overhead from the off shore ridge, the moisture and heavy rain axis looks to be focused more in the Saint Lawrence River Valley and southern Canada most of today. However, as the leading edge of the low and mid-level southerly jet and impressive PWAT plume noses into the Northeast late this morning into the afternoon, high res guidance shows a few scattered showers and weak thunderstorms tracking into the southwest Adirondacks and western Mohawk Vally. Warm/moist mid-levels will keep lapse rates poor, limit instability and therefore likely prevent any severe storms.

The heavy rain/moisture axis from the Saint Lawrence River Valley shifts eastward tonight into eastern NY and western New England as the northern stream trough takes on a negative tilt. The favorable overlap of strong forcing for ascent, weak instability and strengthening southerly flow through a deep layer within a highly moisture rich environment will support high rainfall rates. The latest PMM from the HREF shows a 30 - 50% chance for over 1" of rain in 3hrs and even a small area with a 10% chance of over 3" of rain in 3hrs during the 06 - 15 UTC Monday window. The highest probabilities and QPF maxima areas are favored in the mid-Hudson Valley into western MA and NW CT, similar to the slight risk Day 2 ERO placement. While bands of heavy rain should be rather progressive, the unidirectional flow through a deep layer suggest potential for heavy rain to repeatedly impact a given area tonight into Monday morning. With 1hr and 3hr flash flood guidance values generally 1.75 - 2.5" here, it will take repeatedly rounds of heavy rain to raise concerns for isolated to scattered flash flooding; however, the impressive moisture anomalies and favorable warm rain processes supporting high rainfall rates means we will need to closely monitor rainfall trends overnight into Monday morning.

The main moisture/heavy rain axis shifts into New England Monday morning as the parent shortwave cuts-off and pushes eastward. However, there is increasing confidence for a line of strong to even severe storms to develop ahead of the sfc boundary as it tracks eastward Monday afternoon. Storms can certainly produce additional heavy downpours as instability increases on Monday and any areas that become saturated from the overnight/Monday A.M rain will be vulnerable to additional localized flooding. Between 8PM Sun and 8PM Mon, the latest NBM probabilistic guidance still shows a 40 to 70% chance for 24hr rainfall amounts to exceed 1" with even a 20 to 35% chance for over 2". The highest probabilities are favored in the Day 2 ERO slight risk (level 2 of 4) area in the mid-Hudson Valley and NW CT; however, these areas mainly missed out on the record rainfall last week so decided to hold off on a Flood Watch in collaboration with neighboring WFOs. A marginal risk (level 1 of 4) in the Day 2 ERO extends further north/west into most of eastern NY where any flash flooding should be isolated.

KEY MESSAGE 2...

After the main area of rain exits into New England Monday morning, there may be a brief opportunity for filtered sun to help destabilize the atmosphere before the main trough axis swings through the region Monday afternoon. The best chance for this looks to be from the Capital District/Upper Hudson Valley eastward into western New England where there will be a few hour delay between the exiting morning rain and the sfc boundary. Given the high dew points/very humid air mass in place, any insolation will quickly increase sfc based instability. However, forecast soundings show a rather moist column so mid-level lapse rates are rather poor. Even still, the fast flow aloft and a veering wind profile in the low-levels will support both directional and speed shear with 0-6km shear values nearing 40kts. This regime looks to favor wet microbursts leading to localized damaging winds from any storms that can grow upscale with sustained updrafts. SPC expanded the marginal risk in its Day 2 Outlook to message damaging wind potential from any severe storms. Given uncertainties on how much insolation can occur before the sfc boundary arrives, a marginal risk for isolated severe storms seems most appropriate. The sfc boundary exits into New England by or shortly after 00 UTC Tues, ending the severe weather threat.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

Through 12Z Monday... VFR conditions prevail across all terminals to start off this TAF period, with southerly winds and some gusty winds up to 15-18 kts at KALB and KPOU. Some lingering low clouds and isolated showers could bring cigs down to MVFR late this morning into this afternoon at KGFL and KPSF, otherwise high clouds will dominate across all terminals through this afternoon. Winds are also expected to strengthen throughout the day today, with gusts expected to reach up to around 20-25 kts at all terminals through this evening.

Scattered showers will begin to move into the region this evening as cigs begin to lower, bringing periods of MVFR vis and cigs to all terminals. This rain will become more widespread after 00Z, causing further reduction in cig/vis categories at all terminals, with the potential of IFR vis at KGFL and KPSF, and IFR cigs at KGFL, KPOU, and KPSF. KALB will also experience these reductions, although vis or cigs are not expected to drop below MVFR at this time, which may change with future TAF cycles.

Outlook...

Monday Night: No Operational Impact. NO SIG WX. Tuesday: No Operational Impact. NO SIG WX. Tuesday Night: No Operational Impact. NO SIG WX. Wednesday: Moderate Operational Impact. Chance of SHRA. Wednesday Night: Moderate Operational Impact. Chance of SHRA...TSRA. Thursday: High Operational Impact. Likely SHRA...TSRA. Thursday Night: Low Operational Impact. Slight Chance of SHRA...TSRA. Friday: Moderate Operational Impact. Likely SHRA...TSRA.

ALY WATCHES/WARNINGS/ADVISORIES

CT...None. NY...None. MA...None. VT...None.